1. Field of the Invention
The invention is related to the field of magnetic storage devices, and in particular, to systems and methods for testing individual sliders for magnetic storage devices.
2. Statement of the Problem
Many computer systems use disk drives for mass storage of information. Disk drives typically include one or more sliders positioned proximate to a storage media. The sliders include read and write elements that read from and write to the storage media. One type of slider includes a Giant Magneto-Resistive (GMR) read element. To read data from the storage media, the storage media spins and magnetic data in the media generates a localized magnetic field. The magnetic field modulates the resistance of a magneto-resistive (MR) element in the slider. The change in resistance of the MR element is detected by passing a sense current through the MR element and then measuring the change in voltage across the MR element. The resulting signal is used to recover the data encoded on the storage media. To write data to the storage media, an inductive element in the slider produces a magnetic field that records the data on the storage media.
Sliders are typically manufactured on a single substrate wafer that includes an array of sliders. The sliders are arranged in rows on the wafer. When cutting the wafer, the wafer is first cut into rows of sliders. While the sliders are in an attached row, the surfaces of the sliders are lapped. The lapping process creates a desired height for the MR element which provides a desired magnetic characteristic for the MR element. The resistance of the MR element to a given magnetic field may reflect the desired magnetic characteristics of the MR element. The sliders are also etched to create a desired air bearing surface (ABS) on each slider to allow the slider to fly a desired height above a storage media. The individual sliders in the attached row are then cut and mounted in a head-gimble assembly (HGA).
One problem affecting performance on GMR read elements is pinned layer reversal. In normal operation of a slider, a magnetic field directed into the ABS of the slider is reflected by a positive change in the resistance of the MR element in the slider. A magnetic field directed away from the slider is reflected by a negative change, consequently, in the resistance of the MR element. With pinned layer reversal, a magnetic field directed into the slider is reflected by a negative change in the resistance of the MR element and a magnetic field directed away is reflected by a positive change. Pinned layer reversal causes the MR element to inaccurately read data from a storage media. Pinned layer reversal may be caused by Electro-Static Discharge (ESD), mechanical stress from manufacturing, mechanical stress from head and disk interaction, handling, or other factors.
Various measurements are developed to verify MR element robustness against pinned layer reversal in either the design or manufacturing phase. For the effect of mechanical stress, a test operator alternates between applying stress to sliders in a row and performing quasi-static measurements. The effect of the stress to the pinned layer reversal is understood by comparing quasi-static measurements before and after each stress application. Sliders are currently tested while they are still in a row. Each slider is first tested one at a time with a quasi-static measurement system. In quasi-static measurements, a first slider in the row is positioned proximate to a magnet and then a measurement system is landed onto conductive pads on the deposit end of the first slider to measure magnetic performances of the MR element in the first slider. After the measurements on the first slider are done, the next slider is moved to the position for measurements. The process repeats until the measurements are performed on each slider along the row.
For applying mechanical stress on each slider, the test operator performs a mechanical stress procedure to apply stress to the sliders with a mechanical stress module. The test operator lands a mechanical probe on a slider at one end of the row. One of the choices for the mechanical probe is a pair of ESD tweezers. The mechanical probe slides along the edge joining the air bearing surface (ABS) and the deposit end of each slider. The sliding motion of the mechanical probe applies mechanical stress to the edge of each slider and consequently applies stress to the MR element in each slider. The amount of stress applied to the edge depends on the amount of weight added to the mechanical stress module. After the stress is applied, the test operator again takes the row out of the mechanical stress module and places it on the quasi-static measurement system for quasi-static measurements on each slider. The test operator alternates between applying mechanical stress to the edges of the sliders with increasing weight, and taking quasi-static measurements to test the MR elements in the sliders. This testing procedure is illustrated below in FIGS. 1, 2, and 3A–B.
One problem with the current testing procedure is that the sliders are tested while the sliders are still in an attached row. It may be desirable to test individual sliders that are not in an attached row, but this is not feasible with the current tester capability because it is very difficult to manually land the current mechanical probe on a slider of a 1 mm width. If a low yield is provided for testing, one should only measure good heads along the row and the overall throughput can be very low. Also, it may be desirable to test sliders with multiple MR element designs at the same time under the same test conditions. This is not currently allowed because sliders in an attached row are inevitably of the same design.
Another problem with the current testing procedure is that the procedure is manual. There is significant manual handling of the sliders between the quasi-static measurements and the mechanical stress procedure which may cause mechanical stress not quantified by the tests. There is also a risk of ESD affecting the sliders. These conditions may negatively affect the accuracy of the tests.
Another problem with the current testing procedure is that the quasi-static measurements are inefficient in that they are performed one at a time on a row of sliders.